How Keto Works

  • Feb 21, 2024
  • By Rikke Svartangen
  • 0 Comment

Keto works by encouraging your body to adapt to burning fat instead of sugar as its primary fuel. This is known as ketosis. 

The sugar we use for fuel comes from the carbohydrates in our food. Things like bread, pasta and other processed foods are all high in carbs. 

Carbohydrates turn to glucose (sugar) in your blood and trigger your body to produce insulin. In turn, this insulin either causes your body to burn the sugar as a fuel or store it as fat.

A ketogenic diet stops this cycle. 

  • In this guide, we’ll look at how it does this and the numerous health benefits that being in a state of ketosis can bring. 

From tips on what to expect when you’re in ketosis and how to stay well once you’re there, we’ve got you completely covered as you begin your journey.

Our Bodies on Carbs

As we outlined above, ketosis is a state in which your body uses fat, rather than sugar, to give you energy.

For the majority of the population, carbohydrates are the main source of fuel. According to a government survey collecting data between 2009 and 2012, the mean intake of carbohydrates as a percentage of their diet was 46% in adults1

The NHS recommends that we eat around 260g2 of carbohydrates everyday to maintain a balanced diet.

But as we’ve just shown you, these carbohydrates turn into sugar and then fat when we digest and store them. A diet based on these foods increases blood-glucose levels and the amount of fat we have in our bodies, which can lead to serious health issues. 

💻 RELATED: We've written more about the effect that carbs have on your body in our article 👉 What is a Low-Carb Diet

What is Ketosis?

When you reduce your carbohydrate intake to under 50g a day, your body produces much less insulin and the sugar stores you have in your body (which are known as glycogen) decrease3. However, the exact level will be different for every person, so it’s generally recommended to stay below 20g of carbohydrates per day4.

At this point, your body will start using fat, including body fat, instead of carbohydrates for fuel. 

This is when ketogenesis begins. 

Ketogenesis is the biological process that creates ketones as an alternative energy source for your body, so that you can continue to function as usual5.

These ketones are made from the fat stored in your body and new fat that you eat. Once you reach ketosis, your cells will use ketone bodies to generate energy for as long as you maintain your ketogenic diet6

The Benefits of Ketosis

As well as being a more efficient way of fuelling your body7, numerous studies show that ketosis – and therefore a low-carb or keto diet – works to have a positive effect on your health and wellbeing.

It can improve your brain function 

The process of ketogenesis produces a ketone called beta-hydroxybutyrate (BHB). Our ability to produce it is potentially the reason for the survival of humans through periods of starvation. It’s even been called a ‘super fuel’8 for our brain and can help support long-term memory function9. The keto diet has also been tested for its ability to slow down or reverse some neurological disorders, like epilepsy, dementia and brain cancers1011.  

It can help you lose weight

You’re burning fat as fuel when you’re in ketosis so you will naturally lose body fat…because that’s how the keto diet works! Research also shows that a keto diet can reduce your appetite, so you might find yourself eating less overall too12

A 12-week study carried out in the US military showed that those who stuck closely to a strict ketogenic diet, when compared with those who ate carbohydrates, lost weight and improved their body composition with no negative effect on their physical performance at all13.

It can help you manage type 2 diabetes

The carbohydrates you eat on the ketogenic diet are very low, which significantly reduces the amount of glucose (sugar) in your blood and reduces any steep rises in your blood-sugar14. Very-low carbohydrate diets have even been shown to reduce the need for antihyperglycemic medications15

Our founder, Eryl Vaughan, has been managing his type 2 diabetes using the keto diet since 2015. Listen to Eryl explain how the keto diet works for him in the video below 👇

It can treat seizures

When the ketogenic diet was first developed in 1921, by Dr Russel Wilder, it was as a therapeutic diet for children with epilepsy. The diet was used by the medical profession until epilepsy drugs were discovered and became more popular16. But that doesn’t negate the positive impact that the keto diet can have on the condition, with the modified Atkins diet (a less restricted form of the classic keto diet) being just as suitable for adults17

How to Get into Ketosis

Be prepared

Starting a ketogenic diet can be a big lifestyle change. Join groups on social media, buy recipe books and research the best keto recipes online. There are thousands of people out there who are on this journey with you. So please never feel alone. It can be helpful to use a meal planner so that you can keep track of what you’re going to eat and when, to make your keto diet easy to keep up with.

Reduce your carb intake

You need to be eating a low- to very-low-carb diet18 to experience the full benefits of a keto diet. This means no more than 20g carbohydrates per day. 

The carbs we’re talking about here are net carbs. If you’re in the UK, the net carbs are most likely the number written on the nutritional information of the food you’re buying. If you’re using US products, you can calculate the net carbs by deducting the amount of fibre in the product from the total carbs.

Where possible, these carbohydrates should come from real food, which is food that’s not processed. Good quality meat, line-caught fish, free-range eggs, raw nuts and vegetables are a great examples of real food.

You can also try low-carb alternatives to your favourite foods. We carefully create and select wholesome, low-carb products so that you can continue to enjoy the things you love while on a ketogenic diet, like pizza, bread and even pasta

Make sure you eat vegetables

…but be aware that not all of them are low-carb. As a quick and easy way to decide which vegetables are low in carbs, a rule of thumb is to opt for vegetables that grow above the ground. 

Avocado, spinach, lettuce, olives, cauliflower, aubergine, courgette and broccoli all have low net-carbs per 100g and so they are all suitable for your low-carb diet..

Raspberries and blackberries are also a great natural low-carb dessert or snack, in moderation. 

Eat more fat!

Yes, this might seem contradictory to all the other dieting advice you’ve had in the past but this is how keto works. It’s important to remember that fat is going to be your fuel going forward, so your body will be burning it off to give you energy. 

In addition to good quality meats and fish, you can get these fats from oils, cheese and butter, avocados and olives, and some nuts (almonds, pecans and macadamia are a great low-carb source of fat).

Monitor your protein intake

You’ll need to be mindful of how much protein you eat while using a ketogenic diet. Eating too little can mean you’re essentially starving your body – and that’s definitely not healthy. This will slow your metabolism and cause you to lose muscle mass, which in turn reduces your strength.

Eating 1g of protein per kilogram of your ideal body weight should give you the right amount of protein per day. So that your keto diet doesn’t become one that starves your body of essential macronutrients, we recommend that you reduce your intake to this number gradually. 

If you weigh 100kg you should be eating 90g of protein a day, and gradually lower in 10g increments.  

Give your body time to adjust

You may be lethargic during the first few days on the keto diet -a feeling that’s often referred to as ‘keto flu’. Maintaining your usual fitness routine might be difficult in this initial period. Once you’re in ketosis that tired feeling should go away and you’ll feel full of energy. 

How do you know if you're in ketosis?

You’ve cut out all the carbs and sugar. You’re eating more fat and moderating your protein. And you’re exercising. So when does it all start?

Studies show that ketosis can take between 1 – 8 days from the start of your keto diet19 – and anything up to one month! 

A few of the tell-tale physical signs are a bad taste in your mouth or bad breath, the need to wee more often and a lower appetite. You might also feel lethargic initially, although your energy levels will soon bounce back20.

Some choose to confirm whether they’re in ketosis by measuring their ketone levels using a urine stick, breath analyser or blood ketone metre. 

The problem with this is that the ideal levels of ketones for you will really depend on why you’ve started the keto diet in the first place, and on any preexisting medical conditions.

Chemicals in your blood are measured in millimoles per litre (mmol/l). If you have anywhere between 0.5-3 mmol/l of ketones in your blood, this is seen as a good level for you to lose weight. Whereas 1.5-3 mmol/l is actually called ‘optimal ketosis’, despite there being evidence of substantially different benefits to having a slightly lower ketone level21.

There are a few positive signs to look out for too.

We said above that you might feel a little lethargic when you start your keto diet. After this initial stage, many people report a feeling of mental clarity while they are in ketosis22. This can be linked back to the body’s production of BHB while in ketosis23.  

As your body begins to burn fat, you might also notice that your clothes become looser and your body shape starts to change. If you’re exercising more as part of your lifestyle switch, this transformation may be even more noticeable. You shouldn’t feel discouraged if the scales don’t move immediately, as your body will still be burning fat —don’t trust the scale, trust your jeans!

Keto diet side effects

Keto flu

One of the most common side effects of ketosis is the ‘keto flu’ or ‘induction flu’. 

The symptoms of ‘keto flu’ will generally appear in the first few days of starting your keto diet. Its symptoms can include headaches, feeling tired, lack of motivation or nausea24

The solution

‘Keto flu’ can also sometimes be confused with sugar withdrawal. But ‘keto flu’ is actually caused by dehydration or salt deficiency, so checking that you drink enough and get enough electrolytes is important. 

Carbohydrates hold on to fluids. When you lower the amount of carbs consumed, these fluids are lost. Electrolytes like sodium, potassium and magnesium are flushed out of your system at the same time.

These electrolytes are essential to many of your body’s biological processes, including proper function of the heart, muscles, nerves…even sleep. A sudden shortage in them can also cause muscle cramps, brain fog, headaches, low energy and digestive issues. 

If you replace these electrolytes, you can easily avoid these side effects and the ‘keto flu’. 

For some people, replacing sodium is as easy as drinking a glass of water with half a teaspoon of salt or others choose to drink bouillon or broth.  Spinach is also a great source of both potassium and magnesium. 


This is often a result of a change in diet. Your body and its gut bacteria are used to you eating a certain way. It’s going to take time for your digestive system to adapt and function efficiently and effectively again25. Constipation can also be caused by dehydration, which is another side effect of ‘keto flu’.

The solution

As well as increasing the fluids and salts you’re taking in, you could also try increasing the amount of keto-friendly vegetables you eat so that you know you’re getting enough fibre26

If you’re still blocked up after these efforts, we recommend magnesium supplements or topping some full-fat yoghurt with milled linseed (which is low-carb) could also do the trick27

Bad breath

Bad breath isn’t pleasant. But it’s actually a reliable sign that you’re in ketosis28. It happens when your liver metabolises fatty acids rather than glucose and produces acetones (a type of ketone) as a by-product29.

The solution

While you can’t counteract the acetone on your breath by brushing, make sure you keep up with good dental hygiene and consider using a fresh breath spray30. As with the other side effects we’ve mentioned, your body will adapt and your bad breath will most likely fade away. 

When you choose to make any significant lifestyle change, you should always speak to your doctor or specialist about how to go about it safely. If you experience any health issues as a result of your keto diet, or you’re worried about anything, make sure you seek professional advice before continuing. 


  1. 2015. Carbohydrates and health. [ebook] TSO (The Stationery Office). Available at: <> [Accessed 5 May 2022].
  2. NHS Reference intakes explained available at (Accessed on 4th March 20220
  3. Masood, Annamaraju and Uppaluri Ketogenic Diet available at on 4th March 2022)
  4. Dyson, P. (2020), Very low carbohydrate ketogenic diets and diabetes. Pract Diab, 37: 121-126. (Accessed on 21st April 2022)
  5. Masood, Annamaraju and Uppaluri Ketogenic Diet available at on 4th March 2022)
  6. Harvard Health Blog Ketogenic diet: Is the ultimate low-carb diet good for you? Available at (Accessed on 4th March 2022)
  7. Masood, Annamaraju and Uppaluri Ketogenic Diet available at on 4th March 2022)
  8. Cahill, Veech Ketoacids? Good medicine? available at (Accessed on 7th March 2022)
  9. Ketogenic diet benefits available at (Accessed on 7th March 2022)
  10. Veech, Chance, Kashiwaya et al. Ketone bodies, potential therapeutic uses available at (Accessed on 7th March 2022)
  11. Masood, Annamaraju and Uppaluri Ketogenic Diet available at on 4th March 2022)
  12. Harvard School of Public Health Diet Review: Ketogenic Diet for Weight Loss available at (Accessed on 7th March 2022)
  13. LaFountain et al Extended Ketogenic Diet and Physical Training Intervention in Military Personnel available at (Accessed on 7th March 2022)
  14. Ketogenic diet benefits available at (Accessed on 7th March 2022)
  15. American Diabetes Association Nutrition Therapy for Adults With Diabetes or Prediabetes: A Consensus Report available at (Accessed on 7th March 2022)
  16. American Diabetes Association Nutrition Therapy for Adults With Diabetes or Prediabetes: A Consensus Report available at (Accessed on 7th March 2022)
  17. Epilepsy Foundation Ketogenic Diet available at (Accessed on 7th March 2022)
  18. Nutrition 2019 Effects of differing levels of carbohydrate restriction on mood achievement of nutritional ketosis, and symptoms of carbohydrate withdrawal in healthy adults: A randomized clinical trial available at (Accessed on 7th March 2022)
  19. Nutrition 2019 Effects of differing levels of carbohydrate restriction on mood achievement of nutritional ketosis, and symptoms of carbohydrate withdrawal in healthy adults: A randomized clinical trial available at (Accessed on 7th March 2022)
  20. Diet Doctor The complete guide to ketosis available at (Accessed on 7th March 2022)
  21. Diet Doctor The complete guide to ketosis available at (Accessed on 7th March 2022)
  22. Diet Doctor The complete guide to ketosis available at (Accessed on 7th March 2022)
  23. Dowis and Banga The Potential Health Benefits of the Ketogenic Diet: A Narrative Review available at on 28th March 2022)
  24. Nutrition 2019 Effects of differing levels of carbohydrate restriction on mood achievement of nutritional ketosis, and symptoms of carbohydrate withdrawal in healthy adults: A randomized clinical trial available at (Accessed on 7th March 2022)
  25. Side effects of a ketogenic diet available at (Accessed on 7th March 2022)
  26. Harvard Health Publishing What is keto flu? available at (Accessed on 7th March 2022)
  27. Public Health Collaboration FAQs: Constipation. Help! available at (Accessed on 7th March 2022)
  28. Musa-Veloso, Likhodii, Cunnane Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals available at (Accessed on 7th March 2022)
  29. Prabhakar et al. Acetone as biomarker for ketosis buildup capability – A study in healthy individuals under combined high fat and starvation diets available at (Accessed on 7th March 2022)
  30. Diet Doctor Low carb & keto side effects and how to cure them available at (Accessed on 7th March 2022)



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